The point kept Schalke on course to finish top of the group with two games to go

Walcott struck after 18 minutes and Giroud eight minutes later as the Gunners chased the win which would have put them a step closer the Champions League knockout stages.

But a goal on the stroke of half-time by Klaas-Jan Huntelaar put Schalke back in it and the comeback was complete when Thomas Vermaelen deflected a Jefferson Farfan shot into his own net after 67 minutes.

But Walcott could have snatched a last-gasp winner when he broke through only to fire straight at keeper Lars Unnerstall.

The point kept Schalke on course to finish top of the group with two games to go.

But Arsenal, who could have gone top with a win, still have work to do with Olympiacos within a point after beating Montpellier 3-1.

The odds did not look promising for Arsene Wenger’s men going into the game. Schalke had lost only two in their last 12 at home in this competition.

Arsenal had been beaten in eight of their last 13 Champions League away games and won only three. Schalke also won comfortably 2-0 at Arsenal a fortnight ago.

The Gunners also arrived in Germany with genuine concern swirling around them after three league defeats in five.

So Vermaelen was moved to left-back and Wenger brought back Laurent Koscielny.

The new-look defence was tested three times in the opening minutes as Schalke broke with pace down the flanks.

Mikel Arteta blocked a shot from Christian Fuchs, Vito Mannone did equally well to get down low to keep out Ibrahim Afellay’s shot and Benedikt Howedes headed over.

Arsenal were not in the game. But in the 18th minute they got a gift and seized it.

Per Mertesacker drilled a hopeful long ball and Roman Neustadter misjudged a header, sending Giroud clean through on goal.

The Frenchman hesitated long enough to allow Howedes to get back and tackle.

But Walcott was lurking and picked up the loose ball, went around the keeper and tapped it into an empty net.

Schalke were forced to make an early change as right-back Atsuto Uchida limped off and Arsenal struck again instantly. Santi Cazorla fed Jack Wilshere on the edge of the area. He was blocked off but fed the ball to Giroud, who found Lukas Podolksi on the left.

The German, booed by home fans every time he touched the ball, turned and put in a great cross for Giroud to round off a fine move by heading in from six yards.

Schalke, backed by great support, poured forward at every opportunity and Farfan was unlucky to see one long-range shot fly just over.

But Huntelaar brought Schalke back into the game right on half-time.

Lewis Holtby flicked a header to Huntelaar unmarked on the left of the area and he shot across Mannone and into the far corner.

Schalke pushed for the equaliser and Farfan’s deflected shot ruined Arsenal’s good start. But the point may still prove vital.